1. Field of the Invention
The present invention relates to a power supply control circuit for memories and a method thereof where in a situation of being mounted on a same chip together with a plurality of memory modules, a power supply to each of these memory modules are controlled per module or per bank in the module and further relates to an apparatus equipped with memories where it becomes possible to control the power supply to each of a plurality of memory modules.
2. Description of the Related Art
With respect to an LSI (Large Scale Integrated Circuit), for example, such as a system LSI, a high-capacity memory was realized generally by mounting a plurality of DRAM (Dynamic Random Access Memory) modules. However, all of these DRAM modules are not always in a used condition as memories and it is an actual situation that the power supply is switched on for the DRAM modules even though they are not being used.
Incidentally, there is shown a technique in a Patent Reference 1 where refreshing intervals of the DRAM are controlled and the refreshing intervals are made possible to be fully prolonged.
<Patent Reference 1>
Japanese Registered Patent No. 3177207
As mentioned above, the power was consumed unnecessarily in the prior art, because the power supply was always switched on also for the DRAM modules which are not in a used condition even though all of the plurality of DRAM modules mounted in the system LSI are not always in a used condition. Generally as a current classification for the DRAM, a refreshing current for rewriting data which are charged in capacitors is to be cited first and there can be cited other than that such as a leakage current of a transistor and the like and a penetrating current in a biasing circuit. However, a fact can not be denied that the power is consumed unnecessarily, because a refreshing operation is performed even though the data are unnecessary or the data are not used for a long time and further because there exists a leakage current or a penetrating current even if a refreshing operation is not performed.